The invention relates generally to methods and apparatus for surveying a condition of an organ of a subject, and particularly to methods and apparatus for surveying the electrical activity of one or more chambers of the heart.
Cardiac arrhythmias, the most common of which is ventricular tachycardia (VT), are a leading cause of death. In a majority of patients, VT originates from a 1 mm to 2 mm lesion located close to the inner surface of the heart chamber. One of the treatments for VT comprises mapping the electrical pathways of the heart to locate the lesion followed by ablation of the active site.
U.S. Pat. No. 5,546,951 and U.S. patent application Ser. No. 08/793,371, which are incorporated herein in their entirety by reference, disclose methods for sensing an electrical property of the heart tissue, for example, local activation time, as a function of the precise location within the heart. The data are acquired with one or more catheters that are advanced into the heart, the catheters having electrical and location sensors in their distal tips. Methods of creating a map of the electrical activity of the heart based on these data are disclosed in commonly assigned U.S. patent application Ser. Nos. 09/122,137 and 09/357,559 filed on Jul. 24, 1998 and Jul. 22, 1999, respectively, which are also incorporated herein in their entirety by reference. As indicated in these applications, location and electrical activity is preferably initially measured on about 10 to about 20 points on the interior surface of the heart. These data points are then generally sufficient to generate a preliminary reconstruction or map of the cardiac surface to a satisfactory quality. The preliminary map may be combined with data taken at additional points in order to generate a more comprehensive map of the heart""s electrical activity. The detailed map so obtained may then serve as the basis for deciding on a therapeutic course of action, for example, tissue ablation, to alter the propagation of the heart""s electrical activity and to restore normal heart rhythm.
Catheters containing position sensors may be used to determine the trajectory of points on the cardiac surface. These trajectories may be used to infer the motion characteristics such as the contractility of the tissue. As disclosed in U.S. Pat. No. 5,738,096, incorporated herein in its entirety by reference, maps depicting such motion characteristics may be constructed when the trajectory information is sampled at a sufficient number of points in the heart. A high quality preliminary map of motion characteristics is dependent on acquiring a sufficient number of points representatively spaced about the heart chamber volume.
In constructing these preliminary maps, it is desirable that the data are sampled at points sufficiently spaced to outline the entire volume of the chamber under study. If the preliminary map adequately outlines the heart volume, acquisition of additional points will generally enable the detailed reconstruction to permit accurate diagnosis and treatment. Occasionally however, incomplete sampling, as, for example, by localizing the sample points to only a portion of the heart volume, will result in the generation of an incomplete map. Further sampling may lead to a more detailed map of the partial cardiac volume, but this may be inadequate for proper diagnosis and treatment.
In creating maps of the heart using the above-referenced systems, the initial data points for the preliminary reconstruction are generally acquired under the guidance of an imaging modality such as fluoroscopy that permits the cardiologist to observe the placement of the catheter tip within the heart chamber. Once the preliminary map is generated, subsequent points may then be acquired under the guidance of the preliminary map and a location system based on, for example, electromagnetic or acoustic sensors. Unfortunately, unassisted fluoroscopy provides relatively poor visualization of topographical features within the heart. While contrast-assisted fluoroscopy, in which a contrast agent is injected into the heart chamber under examination, significantly improves the observation of topography, the contrast agent obscures the observation of the catheter tip. Thus, fluoroscopy is insufficient to properly guide the cardiologist to the points on the interior of the heart necessary for the generation of a preliminary map of the electrical activity that roughly encompasses the complete heart volume. The potentially harmful effects of ionizing radiation to the patient also limit the amount of data that can be collected under fluoroscopy.
Electrical activity at a point in the heart is typically measured by advancing a catheter containing an electrical sensor at or near its distal tip to that point in the heart, firmly contacting the tissue with the sensor and acquiring data at that point. Alternatively, electrical activity may be measured with catheters containing multiple electrodes.
It is generally important to maintain good electrical contact between the electrodes and the tissue in order to obtain a reliable and stable electrical reading. Fluoroscopy produces images that are lacking in topographical detail. Accordingly, in taking measurements under the guidance of this imaging modality, the catheter tip may not actually be in effective contact with the tissue. Alternatively, it may be possible to bruise the intracardial tissue by excessive pressure of the catheter tip against the tissue while making such measurements.
The present invention is directed to a method for intracardially surveying a condition of a chamber of a heart of a subject. The method of the invention is accomplished by use of a catheter having a distal tip with a condition sensor contained therein or proximate thereto. The condition sensor is capable of sensing condition information of the heart chamber. The method of the invention comprises the steps of:
a) acquiring a first image of the chamber which contains topographical information of the chamber;
b) advancing the catheter distal tip into the chamber;
c) acquiring a second image comprising a representation of the catheter distal tip in the chamber;
d) displaying a superposition of topographical information acquired in step (a) with the second image of step (c) to generate a displayed superimposed image comprising representations of the topographical information and the catheter distal tip;
e) acquiring condition information at an acquisition point on the chamber with the condition sensor, the acquisition point being selected from points on the displayed superimposed image of step (d) proximate the topographical information;
f) repeating step (e) at one or more additional acquisition points, the points being sufficient in number and spacing throughout the chamber to permit the generation of a survey map of the condition in the chamber.
In a preferred embodiment, the method of the invention comprises the steps of:
a) acquiring a first, contrast-assisted fluoroscopic image of the chamber;
b) creating a contour image of the interior of the chamber from the contrast-assisted fluoroscopic image;
c) advancing the distal tip of the catheter into the chamber;
d) acquiring a second, non-contrast-assisted fluoroscopic image comprising a representation of the catheter distal tip in the chamber. The first image and the second image are acquired from a common projection relative to the subject;
e) displaying a superposition of the contour image of step (b) with the fluoroscopic image of step (d) to generate a superimposed image;
f) acquiring condition information at an acquisition point on the chamber with the condition sensor, the acquisition point being selected from points on the displayed superimposed image of step (e) proximate the topographical information;
g) repeating step (f) one or more times at one or more additional acquisition points, the points being sufficient in number and spacing throughout the chamber to permit the generation of a survey map of the condition in the chamber.
In another preferred embodiment, the method of the invention comprises the steps of:
a) acquiring a first, contrast-assisted fluoroscopic image of the chamber, the first, contrast-assisted fluoroscopic image being acquired from a first projection relative to the subject;
b) creating a first contour image of the interior of the chamber from the first contrast-assisted fluoroscopic image;
c) acquiring a second, contrast-assisted fluoroscopic image of the chamber, the second, contrast-assisted fluoroscopic image being acquired from a second projection relative to the subject;
d) creating a second contour image of the interior of the chamber from the second contrast-assisted fluoroscopic image;
e) advancing the distal tip of the catheter into the chamber;
f) acquiring a first non-contrast-assisted fluoroscopic image comprising a representation of the catheter distal tip in the chamber, the first non-contrast-assisted fluoroscopic image being acquired from the first projection relative to the subject;
g) displaying a superposition of the first contour image of step (b) with the first non-contrast-assisted fluoroscopic image of step (f) to generate a first superimposed image;
h) acquiring the condition information at an acquisition point on the chamber with the condition sensor, the acquisition point being selected from points on the displayed superimposed image of step (g) proximate the first contour image;
i) acquiring a second non-contrast-assisted fluoroscopic image comprising a representation of the catheter distal tip in the chamber, the second non-contrast-assisted fluoroscopic image being acquired from the second projection relative to the subject;
j) displaying a superposition of the second contour image of step (d) with the second non-contrast-assisted fluoroscopic image of step (i) to generate a second superimposed image;
k) acquiring the condition information at an acquisition point on the chamber with the condition sensor, the acquisition point being selected from points on the displayed superimposed image of step (j) proximate the second contour image;
l) repeating steps (h) and (k) at one or more additional acquisition points, the points being sufficient in number and spacing throughout the chamber to permit the generation of a survey map of the condition in the chamber.
In another preferred embodiment, the method of the invention further comprises the step of marking the display of the superimposed image to identify the points on the chamber on which the condition information was acquired.
The invention is also directed to apparatus for intracardially surveying a condition of a chamber of a heart of a subject. The apparatus of the invention comprises:
a) means for displaying a superposition of topographical information from a first acquired image with a second image; and
b) means for acquiring condition information at a number of points in the chamber, the points being sufficient in number and spacing throughout the chamber to permit the generation of a survey map of the condition in the chamber.
In a preferred embodiment, the apparatus of the invention further comprises means for marking the display to identify the points in the chamber at which the condition information was acquired.
In another preferred embodiment, the apparatus of the invention further comprises means for generating the topographical information from the first image.
It is an object of the invention to provide a method for surveying a condition of a chamber of the heart to permit the generation of a preliminary map of the condition in the chamber.
It is another object of the invention to provide a method for surveying a chamber of the heart that avoids collection of data localized in only a portion of the sampling volume.
It is another object of the invention to provide a method for surveying the condition of a chamber of the heart to permit the reconstruction of detailed maps that enable more accurate diagnosis and treatment of the heart.
It is another object of the invention to provide a method for surveying a chamber of the heart that reduces the likelihood of injury to heart tissue during sampling of the condition data.
It is another object of the invention to provide a method for surveying a condition of a chamber of the heart that minimizes the adverse effects of ionizing radiation during collection of the survey data.
It is another object of the invention to provide a method for surveying a condition of a chamber of the heart that provides the capability to mark the displayed information to indicate the points on the heart at which such information was acquired.
It is another object of the invention to provide an apparatus to survey the condition of a chamber of the heart in a process that possesses the above-enumerated attributes.
These and other objects, features and advantages will be more readily apparent from the detailed description set forth below, taken in conjunction with the accompanying drawings.